Method and system for a micro-channel bank for providing voice, data and multimedia services in a wireless local loop system

ABSTRACT

A method and system provides for removing a number of channels from a larger pool of channels. The channels are assigned in ways to provide subscribers with both voice and digital data service. The system is designed to support POTS ISDN, and direct data service in a point to multipoint configuration. Channel concatenation provides a multiplicity of channels. The system utilizes frequency division duplex (FDD) operation so as to double capacity.

This is a continuation of application Ser. No. 09/085,262 filed May 26,1998, now U.S. Pat. No. 6,131,012.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to application Ser. No. 09/085,263, entitledMethod and System for an Air Interface for Providing Voice, Data, andMultimedia Services in a Wireless Local Loop System, filed concurrentlyherewith, now pending, and to application Ser. No. 09/085,264, entitledMethod and System for Protocols for Providing Voice, Data, andMultimedia Services in a Wireless Local Loop System, also filedconcurrently herewith, now pending. Each of these applications isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the implementation of wireless systemsin a local telephone loop environment in what is usually called aWireless Local Loop (WLL). The present invention particularly addressesthe air interface and protocols used in the implementation of a WirelessLocal Loop.

BACKGROUND OF THE INVENTION

The local loop of a telephone system is what some have termed the “lastmile” or the “last 1000 feet”. This local loop is essentially the copperwire that connects the customer premises (ie, a house or business) tothe telecommunications network. The cost of laying down the copper wirecan be very expensive (ie, over $1 per foot). Where communities arerural in nature as in some parts of the United States or in developingcountries, laying down such an infrastructure can be prohibitivelyexpensive.

As an alternative to installing a wire or cable infrastructure, theserural communities are turning to wireless solutions for theirtelecommunication needs. However, conventional wirelesstelecommunication technologies suffer from a number of disadvantages.Often times, because of the quality of the service, modem connectionsare frequently difficult to establish and maintain. Even where modemconnections are possible, data rates are often prohibitively slow.

A further disadvantage of conventional wireless telecommunicationtechnologies relate to their inefficient use of their RF spectrumresources. Subscribers transferring data over the network occupychannels that would otherwise be available for voice communication. Ininstances in which many subscribers are, for example, accessing theinternet, these conventional wireless technologies suffer from a seriousdegradation in Grade of Service (GOS) resulting in an increase in thepercentage of calls blocked (i.e., Erlang B).

These deficiencies are particularly troublesome in view of the fact thatdata usage is bursty in nature. Analysis of internet data usageindicates that approximately 95-97% of the time, the data network isidle. Furthermore, the aggregate throughput to a user is typically lessthan 5 kilobits per second.

Therefore, there is a need for a wireless telecommunication system toreplace the local loop which more efficiently allocates resourcesbetween voice and data communications yet maintains a desirable highGOS.

The following U.S. Patents are made of record for teaching variousaspects of wireless telecommunications.

In U.S. Pat. No. 5,239,673, issued Aug. 24, 1993, entitled “Schedulingmethods for efficient frequency reuse in a multi-cell wireless networkserved by a wired local area network,” Natarajan describes communicationmethodologies that realize an efficient scheduling and frequency reusein a wireless communications network that is served in a wired network.

In U.S. Pat. No. 4,639,914, issued Jan. 27, 1987, entitled “WirelessPBX/LAN system with Optimum Combining,” Winters discloses a wireless LANsystem that employs adaptive signal processing to dynamically reassign auser from one channel to another.

In U.S. Pat. No. 4,837,858, issued Jun. 6, 1989, entitled “SubscriberUnit for a Trunked Voice/Data Communication System,” Ablay et al.disclose a trunked voice/data subscriber that operates in either a voicemode or one of three data modes.

In U.S. Pat. No. 4,852,122, issued Jul. 25, 1989, entitled “Modem Suitedfor Wireless Communication Channel Use,” Nelson et al. disclose awireless communication system and, specifically, a modem thatcommunicates digital data with data terminal equipment.

In U.S. Pat. No. 5,603,095, issued Feb. 11, 1997, entitled “Radio Systemand a Subscriber Terminal for a Radio System,” Uola discloses a wirelesslocal loop system having at least one exchange, at least one subscriberdatabase and base stations, and subscriber terminals communicating withthe fixed network via a radio path.

In U.S. Pat. No. 5,555,258, issued Sep. 10, 1996, entitled “HomePersonal Communication System,” Snelling et al. disclose a wireless,in-house telephone system designed to provide multi-line telephoneoperations, allowing the consumer to set up a multiple telephone,multiple line system without having to use wired phone connectionsrunning throughout the building.

In U.S. Pat. No. 5,689,511, issued Nov. 18, 1997, entitled “DataReceiver for Receiving Code Signals Having a Variable Data Rate,”Shimazaki et al. disclose a data receiver capable of identifying thecode rate of received data and decoding the data at an adequate ratewithout resorting to a data buffer or a plurality of decoding circuits.

In U.S. Pat. No. 5,504,773, issued Apr. 2, 1996, entitled “Method andApparatus for the Formatting of Data for Transmission,” Padovani et al.describe a data format which facilitates the communication of varioustypes of data, and data of various rates, to be communicated in astructured form.

In U.S. Pat. No. 5,511,067, issued Apr. 23, 1996, entitled “LayeredChannel Element in a Base Station Modem for a CDMA CellularCommunication System,” Miller describes a layered channel softwareelement which supervises the operation of channel element modemresources in a CDMA cellular telephone system that includes forwardchannels for conveying message and signalling data from a CDMA systembase station to mobile units and reverse channels for conveying messageand signalling data from mobile units to base stations.

Wireless local area networks (WLAN) have been available for connectingvarious computers in a local area. However, such systems have not beenappropriate for application on the scale of a local loop. The method oftransmitting and receiving signals in WLAN's is not appropriate for thelarge distances and varied weather conditions encountered in a localloop scenario. Wireless local area networks have the furtherdisadvantage that they cannot carry voice information appropriate for atelephone system.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a wireless telecommunicationsystem that allows individual subcribers in an area of service seamlesstelecommunications access (i.e., POTS (plain old telephone system), ISDN(Integrated Services Digital Network), data, multimedia, etc.) to atelecommunications network. This system facilitates full voice, data,and fax utilization. This system is designed to replace existing localloops or provide infrastructure for those communities with no local loopin place.

These and other objects are achieved by a wireless local loop (WLL)comprising a first interface connecting the WLL to thetelecommunications network, a second interface connecting the WLL to aplurality of customer premise equipment (CPE) such as telephones, faxes,and computers, and point to multi-point radio frequency (RF)communications channels connecting the first interface to the secondinterface. The multi-point RF communication channels provide the userwith traffic/bearer data, user control data and radio link specificoverhead and control. Traffic bearer data may include the use's encodedvoice or data signal. User control data may include ISDN (IntegratedServices Digital Controller) D-channel, translated CAS (ChannelAssociated Signaling) or OAM&P (Operations, Administration, Maintenance& Performance). Radio link overhead and control may include powersettings, timing and framing. The present invention makes improvementsto the WLL system while not requiring substantial changes to thetelecommunications network or the customer premise interface (CPI).

It is a further object of the present invention to provide concentratedaccess to the telecommunications network to buildings, campuses, orsimilar organizations in the area of service that are expected to havehigh telecommunications traffic demand. This and other objects of theinvention are achieved by a capability referred to as “embeddedconcentrated access” which allows the removal of a specified number ofchannels from the pool of multi-point RF communication channels andassigns them to the high traffic demand structure. These removedchannels are referred to as the “micro-channel bank.” The micro-channelbank provides the high traffic demand structure with traffic/bearerdata, user control data and radio link specific overhead and control.The micro-channel bank is assigned to an enhanced radio unit (ERU)attached to or associated with the high traffic demand structure. TheERU provides traffic messaging and bearer channels to a micro-channelbank via the digital radio link (DRL). The remaining multi-point RFcommunication channels provide an acceptable grade of service (GOS) tothe other subscribers in the area of service.

It is a further object of the present invention to provide for dynamicpool sizing of the various channels in the WLL. As the usage conditionsof the WLL change, the size of the various pools of channels can bedynamically changed to meet the differing conditions. Such dynamic poolsizing can be used upon system initialization to get all the subscriberunits on the system operational as quickly as possible. Dynamic poolsizing can also be used to improve overall system performance duringadverse weather conditions so as to increase the processing gain of thesystem.

It is a further object of the present invention to provide thesubscriber with a fast and efficient wireless data interface. This andother objects of the present invention are achieved by a capabilityreferred to as “embedded data access.” The present inventionadvantageously uses subscriber usage statistics (data usage is idleapproximately 97% of the time) to allow a large group of subscribersshared access to a smaller pool of RF traffic channels. The systemperforms at a grade of service (typically 1% in the United States)related to percentage of calls blocked (i.e. Erlang B). The managementof N subscribers in a smaller pool on M available channels is called“concentration” or “trunking” with a concentration ratio of N/M>1.Concentration is one further aspect of the present invention.

Through the use of an interface at the subscriber premises, a directdata access protocol can be utilized to provide the subscriber with afast and efficient wireless data interface. Such an interface would notuse consumer-type modems to achieve such data communications. This wouldeliminate the requirement that each user be assigned one particularchannel. Rather, several data users could use one data channel whilestill achieving similar or better performance as compared to ahigh-speed modem.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention are better understood with reference to the followingdescription, appended claims and drawings where:

FIG. 1 is a diagram of the different components of a WLL systemaccording to the present invention;

FIG. 2 is a simplified diagram of WLL with respect to a singlesubscriber according to the present invention;

FIG. 3 is a mapping of the present invention to an OSI protocol stack;

FIG. 4 illustrates delays associated with forward error correctionaccording to the present invention;

FIG. 5 illustrates an interleaver structure according to the presentinvention;

FIG. 6 illustrates a top level time division duplex (TDD) burst framestructure according to the present invention;

FIG. 7 illustrates a top level concatenated FDD operation according tothe present invention;

FIG. 8 is a detailed diagram of three types of frame structuresaccording to the present invention including the extension of a guardband;

FIG. 9 provides an example of pool allocations for a singlesector/frequency implementation according to the present invention;

FIG. 10 is a flowchart of the Subscriber Receiver Synchronizationprocedure according to the present invention;

FIG. 11 is a flowchart of the Subscriber Transmitter Synchronizationprocedure according to the present invention;

FIG. 12 is a flowchart of the Authentication procedure according to thepresent invention;

FIG. 13 is a flowchart of the procedure to establish incoming calls overthe Basestation Control channel according to the present invention;

FIG. 14 is a flowchart of the procedure to establish outgoing callsaccording to the present invention;

FIG. 15 is an illustration of the TDD frame structure with a time scaleto show the details of the timing of a received TDD frame and atransmitted TDD frame according to the present invention;

FIG. 16 is a flowchart of the TDD acquisition protocol according to thepresent invention;

FIG. 17 is an illustration of the CDMA acquisition hardware of thepresent invention; and

FIG. 18 is an illustration of the fragmentation of a message for propertransmission according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following is a brief description of the wireless local loop (WLL)system of the present invention. The numerical examples provided areprovided as examples and are not meant to limit the scope of theinvention.

FIG. 1 shows the different components of a WLL system. The WLL systemreplaces and/or supplements the copper wire local loop of a typicaltelephone system. In FIG. 1, the WLL is essentially bounded by thenetwork interface 100 and the customer premise interface 102 for singlesubscribers or the network 100 and the micro-channel bank (MCB) 104 fora pooled channel system. The various items in between, thus constitutethe WLL system. The improvements of the present invention deal inparticular with the interface between the basestation 404 and the radiounit (RU) 106 or the enhanced radio unit (ERU) 108.

FIG. 2 provides a simplified diagram of a WLL interface with respect toa single user where the WLL system. is bounded by the network interface200 including a basetation and the subscriber WLL interface 202including radio unit 204 and customer premise interface 206. By allowingfor various individual users that communicate with a single base station404, the WLL thus provides point to multi-point RF wirelesscommunications.

The following describes various considerations and improvements for theimplementation of a wireless local loop system.

Frequency Planning: Co-Channel Interference

The capacity of a cellular wireless system (i.e. the number and densityof users that can be serviced) is heavily influenced by the cell channelfrequency reuse plan, use of sectored antennas, and the minimum signalto interference ratio (SIR) of the RF modulation. Co-channelinterference (CCI) from adjacent cells represents a fundamental issue insystem design and deployment.

In general, deployment of a WLL system with a maximally efficientfrequency and cell plan is desired thus allowing system deployment withminimal spectral occupancy. Additional capacity can be gained by“stacking” additional channel groups (clusters) to increase frequencyuse and capacity by two, three or more times. While it is possible todeploy a system with a frequency reuse of one (i.e. all cells use thesame frequency) in a CDMA system, the CDMA channel capacity must bereduced so that excess processing gain is available to combat theco-channel interference.

Cell reuse factors, N, of three and seven are the smallest possiblewhile 12, 13, and 19 are unreasonably large. The use of sectoredantennas can further improve performance by limiting the number ofadjacent cells that project power directly into the receiver. For areuse factor of three, 120 degrees sectors can be used. For a cell reusefactor of seven, both 120 and 60 degree sectors can be used.

Table 1 summarizes the performance of 3 frequency/1 sector and a 3frequency/3 sector frequency reuse plans where n in the table equals theRF path loss. Note that an SIR of 13 dB is required for a bit error rate(BER) of 10⁻⁵ with DQPSK modulation, for almost any deployment whereideal propagation exists (i.e., N=2). Forward error correction isrequired for this purpose. Frequency reuse of three without sectorantennas is generally not viable. The most spectrum efficient cell planwould be the deployment of three channels with three 120 degree sectors.Proper planning and installation of the basestation antenna (minor tiltdown) can ensure that the RF path loss is greater than or equal to 2.7(ie, 10 dB SIR).

TABLE 1 Frequency/ Sector SIR for n = 4 SIR for n = 3 SIR for n = 2 3/111.3 dB  6.5 dB 1.7 dB 3/3 16.1 dB 11.3 dB 6.5 dB

A great advantage of a DSSS CDMA systems is the ability to reduce thenumber of active CDMA traffic channels to maintain a minimum bit errorrate quality of service at the expense of higher blocking probabilities.In this manner while the number of channels available to subscribers isreduced, because of the increase in processing gain, the quality of theremaining channels is increased thus reducing the bit error rate (BER).BER and signal quality measurements at the base station are used tomanage the available traffic pool and make changes when appropriate.

Adjacent Channel Interference

Another consideration in implementing the present wireless local loopsystem is adjacent channel interference (ACI). ACI is the result ofactive transmitters that lie outside of the occupied frequency band. Thesource of ACI is either the WLL system's own cellular reuse frequencychannels or active signals from other systems.

ACI can be minimized by careful filtering (at both the transmitter andreceiver) and by appropriate channel assignment within the WLL servicearea. In the ISM (Industrial Scientific and Medical) band, adjacentunlicensed users are always present. A strategy of filtering in depth,using digital base band pulse shaping combined with SAW IF filtering,can provide between 60 and 70 dB of Adjacent Channel Rejection (ACR).Raised cosine (RC) finite impulse response (FIR) filters and half-bandfilters have been found appropriate where the choice depends onparticular regulatory requirements and system specifications such asfrequency cutoffs and bandwidth.

System Capacity and Grade of Service (GOS)

The grade of service (GOS) is a measure of the ability of a user toaccess a concentrated system during the busiest hour based on customerdemands. In the United states and other developed countries during thebusiest hours, the traffic intensity of home users is approximately 0.07Erlang (4.2 minutes per hour which is usually three to four short calls)while a business user represents about 0.1 Erlang. The GOS is generallybased on a percentage of calls blocked or Erlang B.

In a system with 24 traffic channels (typical for the presentimplementation of a TDD CDMA); Table 2 provides the number of users thatcan be supported with 1% and 2% GOS given 0.07 Erlang of trafficintensity at the peak usage time. Numbers are provided for a singlesector. Note that in the ISM band it is possible to support 22 channelsor 7 clusters with 3 frequencies per cluster. Although the ISM band ismentioned here, the present invention is not limited to the ISM band.

TABLE 2 Cluster/Sectors/ Channels Users at 1% GOS Users at 2% GOS 1/1/24218 237 1/3/72 655 711

A typical user in the United States tolerates a 1% GOS but not muchworse. However, users in developing nations may tolerate 2% or even upto 5% GOS meaning that a WLL system as described herein could supportmany more users in developing nations. Furthermore, while many moreusers are being supported, the voice and data quality is notcompromised. In this manner, a developing community may be able toimplement the infrastructure for a high quality telephone and datasystem to serve a large number of sparsely distributed customers at avery low cost. Clearly, all these are desirable qualities.

One capability beyond the standard channel subscriber station (single,dual channel, or single/dual channel with a data interfaces) is theconcept of the Micro-Channel Bank (MCB). The MCB uses between 1 and MCDMA channels where M is typically between 3 and 8. When these channelsare in use by the MCB, they are removed from the overall CDMA channelpool resulting in reduced concentration efficiency and/or lower GOS forthe individual subscribers. For the MCB concept to be effective and toreduce cost, the concentration efficiency in the limited pool of Mchannels must be relatively close to that of the system as a whole. Toachieve this goal, the architecture of the MCB and associated interfacesmust provide for dynamic addition of CDMA channels based on subscriberdemand. Channels are not “nailed up” or fixed to a particular serviceand are, therefore, available as usage demands change. Furthermore,increased voice compression can be utilized to increase the number ofchannels and, hence, the concentration efficiency. With such voicecompression, the data rate can be reduced from 32 Kbps to 16 Kbps toincrease the concentration efficiency at the cost of reduced voicequality. Furthermore, not only could every subscriber be aggregated tovoice channels, but the subscribers could also be aggregated to datachannels so as to provide an embedded virtual local area network.

While the discussion thus far has concentrated on voice service as animplementation of the present invention, the reader is reminded that thepresent invention also allows for excellent data service on the samesystem at the same time.

Without modification to the voice service implementation describedabove, a user desiring data service may use a high speed modem. Becausea modem uses modulation techniques that implement frequencies in thevoice range, such a modem would work satisfactorily using the voiceservice. While such an implementation would function adequately, thereis much waste that is undesirable. Typically, internet use results in97% idle time with short periods of high transfer rates where theaverage data transfer rate is approximately 5 kilobits per second. Sucha scenario results when a user accesses a web site with variousgraphics, text or sound which are downloaded upon access of the website. At this point, high transfer rates are experience. Once the neededinformation is downloaded to the user's computer, there can be largeperiods of idle time where the user may be reading or observing the website. During the idle time, there is typically very little, if any, datatransferred. However, during this time when a modem is used, an entirechannel is removed from service for large periods at a time typicallymeasured in hours not minutes as compared to regular voice service. Dataservice in this manner thus greatly increases the Erlangs persubscriber. In a WLL implementation where CDMA channels are a limitedresource, a data implementation using a typical modem is highlyundesirable.

By way of example only and not to limit the scope of the presentinvention, allowing 4 to 6 users to sequentially access one CDMA datachannel instead of those 4 to 6 users removing 4 to 6 CDMA channels forextended periods of time, concentration efficiency is increased. Theremoval of 4 to 6 users using modems removes 17% to 25% of the availablechannels (assuming 24 available channels) while the data implementationof the present invention allows for 4 to 6 users to remove only 4% ofthe channels (1 channel out of 24 typical channels). A properly designedWLL system as described herein can provide a direct data interface tothe subscriber and to the network and retain an adequate concentrationefficiency. In effect, the present invention allows for the unique andbeneficial implementation of a local area network (LAN) on a system thatsimultaneously provides full-featured voice service.

In implementing LAN on a WLL system, there are various considerations toresolve including media access control (MAC) protocol options. Where theLAN concept involves various users sharing a physical link (ie, wired,fiber optic, or wireless), there needs to be a proper implementation ofa MAC protocol access algorithm that allows for: packet access;collision avoidance and collision detection; error detection and dataretransmission; and, flow control/backoff/holdoff to maintain stability.Furthermore, because the packet structure of a WLL system is notoptimized for the typically long LAN packets, a method must beimplemented that provides for fragmentation of LAN packets into packetsappropriate for a WLL system. The fragmented packets can then beencapsulated with appropriate MAC data information including: packetlength; ACK/NACK; a virtual or short interval address corresponding to aphysical address; Cyclic Redundancy Code (CRC); and, Flow Control.

An implementation of a LAN on a WLL system involves uncoordinated userscompeting for the use of a shared channel. The WLL introduces problemsthat eliminate the use of certain multiple access protocols. Inparticular, neither pure ALOHA nor slotted ALOHA is particularly wellsuited because multiple user contentions for a single channel wouldcause high amounts of access noise, thus reducing the performance of thewhole system. However, a polled or token ring system in which thevarious users take turns sending data is appropriate for the LAN of thepresent invention. Such an implementation is very stable where everyuser is provided with a fixed time slot in which the user is allowedaccess to the data channel. As an extension of the token ring protocol,a demand access or reservation protocol may also be implemented thatwould provide further options to the LAN. Demand access and reservationallows for maximum and efficient use of the available bandwidth. Theadded complexity in the MAC algorithm is balanced by its many benefitsincluding its stability under all conditions.

In providing data service, the present invention requires the use of adedicated data interface at the customer premises where such a datainterface functions much as a regular telephone interface. The presentinvention further uses a modified CDMA channel to more efficientlytransfer data at a high rate. The network interface as shown in FIG. 1would thus also provide for a network data interface. The customer isprovided with specially modified software that negotiates the InternetProtocol addresses with “virtual” addresses so as to more efficientlyallow sequential access to the various data users.

In implementing the LAN on the WLL of the present invention, efficiencyis sought wherever possible including efficient messages and responsesto the subscriber station in the subscriber gaining access to the datachannel. Inefficiencies must be reduced in the turn around gap where thesubscriber is sent a message requiring a response as to whether thesubscriber is to respond to a token on the next transmission. Immediateresponse is necessary. Furthermore, alignment problems must be resolvedby providing control packets that are sent only at 2 ms transmissions.

The LAN must make extensive use of media access control (MAC) packets tomake more effective use of bandwidth. As an example, ACK and tokens maybe combined in a single access packet. Dynamic packet sizes are alsoallowed. “Frame to next slot” messages, which define the number offrames to the next slot, may be embedded in the basestation header intransmission to the subscriber station. The basestation can use thepacket header to broadcast 2 ms slots and address of the next subscriberin a MAC encapsulated header. Here, the basestation has more data andlonger packets to transmit to the subscriber stations and thesubscriber-to-basestation messages are short. Subscriber access time iswasted in the time waiting for the basestation to complete broadcastingthe token.

The present invention thus allows for the dynamic assignment of voiceand data channels on an as-needed basis. Where more users require dataaccess, more data channels may be assigned. Or, where more users desirevoice service, more voice service may be assigned. Through this dynamicsizing of voice and data service, much more and better service isprovided than in a situation where the channel assignments are fixed.

CDMA Implementation Issues

While no system is ideal, the present invention incorporates the variousspecific benefits and limitations in implementing a CDMA system.

The CDMA channel capacity is limited by self noise.

For N CDMA channels, the maximum utilization is typically 75 to 85% inreal-world RF conditions. Therefore, in an ideal 32 channel CDMA systemonly approximately 24 channels are actually available for voice or dataservice. In the present invention, the flexibility of CDMA is utilizedto dynamically restrict the pool of traffic or data channels to combatnoise. Where there may be an inappropriate amount of noise when all 32channels are used for traffic, by reducing the channels, the self noiseis reduced with an increased processing gain.

The present invention further takes advantage of processing gain in aunique manner. For voice service, it is obvious that a pair of channelsis necessary—one to speak (transmit) and one to listen (receive).Because of self alignment and perfect power level of all channels at thebasestation, the basestation to subscriber station link has lower selfnoise and thus greater capacity. Basestation to subscriber performancetypically needs less, if any, processing gain as compared to subscriberto basestation transmissions. Furthermore, very low complexity broadcastaccess can be used by the basestation to subscriber station link withtoken and ACK/NACK embedded in the packet stream.

Because voice service necessarily uses pairs of CDMA channels, the samereduction in basestation-to-subscriber and subscriber-to-basestationchannels is necessary so that a symmetry exists. In a data servicesituation, such a symmetric channel pair is not necessary. The presentinvention, through dynamic pool sizing, is able to optimize performanceby reducing subscriber-to-basestation and basestation-to-subscriberchannels independently. Because of the physics of subscriber andbasestation transmissions, more basestation-to-subscriber channels canbe achieved than subscriber-to-basestation channels. Asymmetrical datachannel assignment is, thus, achieved.

A typical data situation occurs where a user makes requests to receiveinformation (i.e. by clicking on a web link) that contain large amountsof text, graphics and sound. Thus, the user sends a small amount of dataand receives a large amount of data—an asymmetrical situation. Theasymmetrical data channel assignment is then very well suited for thistype of scenario. Thus, the present invention makes use of everyavailable channel that can be established regardless of whether it ispaired with another channel.

In further considering CDMA implementations of the present invention,power control of the subscribers is related to access noise and has alarge impact on system capacity. In general, TDD systems have a distinctadvantage over FDD systems because receiver power measurements can bedirectly applied to transmitter power output with low rate minoradjustments to and from the basestation. In contrast, FDD requires fullcommand by the basestation to the subscriber station as transmitter andreceiver links are uncorrelated. Note that in the presentimplementation, subscriber transmitter power should be kept within+/−0.5 dB and that power control must handle fade rates of up to 25dB/s.

TDD further allows for subscriber-only diversity antenna techniqueswhich improve performance in a high multi-path environment. Receiverdiversity measurements and diversity switching can be directly appliedto the transmitter. Note that receiver power measurements must beapplied to the transmitter power output. Directional antennas at boththe subscriber and basestation provide significant reduction inmulti-path and cell to cell AGI and CCI. Beam steering, “smart” antennascan be deployed for further system improvement.

OSI Model

FIG. 3 provides a mapping of the sub-sections to the OSI model. Thepresent invention corresponds to the Physical 610 and Link 612 layers inthe OSI protocol stack. The present invention can be described in alogically ascending order using this model. Radio Frequency 600considerations are discussed first followed by Modem/CDMA 602, ForwardError Correction 604, TDD Frame Structure 606 and finally Access/LinkControl Protocols 608. Where and the subscriber to base (“uplink”)interfaces, those differences are noted.

In the sections to follow, the physical interface is discussed includingthe RF specifications and the packet structure. The various protocolsinvolved in the present invention are then addressed includingacquisition, call set-up, data service set-up.

Physical Layer RF Specification

Based on customer requirements and regulatory authorization, the presentinvention can be deployed in various RF bands. For the presentimplementation, the ISM band is used as an example. The principal designissues for 1.5 to 6 GHz deployment are availability of low cost RFchipsets, and increased phase RF oscillator phase noise and PPM driftlimitations.

Given the RF specifications of the present implementation, one skilledin the art understands that changes can be made to fit a particularimplementation. As an example of an implementation in the ISM band,Table 3 provides the RF specifications as used in the presentimplementation. Note, however, that the present invention can beimplemented in many appropriate frequency bands such as the ISM band at2.4 GHz.

TABLE 3 TX/RX Channel 3.5 MHz nominal Bandwidth TX channel Raised cosinewith 32.5% excess bandwidth. filter 3.4 MHz with 50 kHz guard band.Minimum 50 dB out of band suppression at TX RF. RX channel CompositeIF/base band filter with better filter/adjacent than 50 dB adjacentchannel interference channel suppression at the band edge. interferenceTX/RX channels 22 channels center frequencies separated by 3.5 MHzChannel 1 F_(c) = 2.403 MHz Channel 2 F_(c) = 2.4065 MHz . . . Channel22 F_(c) = 2.480 MHz (Note: Excess guard band at both ends of band tomeet ETSI/FCC forbidden zone emissions) Compliance FCC Part 15.247, ETSIres 10 (Note: Processing gain test port must be provided forcompliance.) Human radiation hazard per ANSIC 95.1 Subscriber <8 CDMAchips from P0 (nominal TX power) TX/RX power to P0 - 20 dB rampBasestation <4 CDMA chips from P0 (nominal TX power) TX/RX power to P0 -20 dB ramp Subscriber 70 dB nominal, 65 dB minimum, 80 dB desiredTransmit power control range Subscriber 70 dB nominal, 65 dB minimum, 80dB desired Receiver AGC Range Basestation RF +/− 2 PPM max. with 0.1 PPMshort term frequency drift variance Subscriber RF +/−10 PPM (cost mayforce this to increase frequency PPM) (Note: Combined +/− 12 PPM resultsin frequency ambiguity which must be resolved via DSP/FFT operations)Temperature of Industrial −40 to +85 deg. C. Operation EIRP 1 Watt max.note: typically 20 to 23 dBm power with 10 to 13 dB antenna gain note: 4W EIRP possible with restrictions TX carrier Better than 25 dB relativeto the peak suppression Sin(x)/x spectrum as measured with 100 KHzresolution bandwidth Spurious Per FCC 15.247, 15.205, and 15.209emissions

Modulation and CDMA Coding

As Modulation and CDMA coding are well known in the area of wirelesscommunications, one skilled in the art understands that changes can bemade to fit a particular implementation. Table 4 provides the modulationand CDMA coding techniques used in the present implementation.

TABLE 4 Symbol Rate Primary rate: 40 Ksymbol/sec (equal to RW repetitionrate) Acquisition/Pilot rate: 2.5 KHz (16 symbols per acquisitionsymbol) CDMA Chip 2.560 Mchip/sec (Note: Burst rate is 2× Rate:aggregate 1.280 Mchip Burst Frame 80 symbols (1 ms burst rate is 2×aggregate Length 1.280 Mchip) Modulation CCITT Gray coded DQPSK:Encoding MSB LSB Phase Change 0 0  0 deg. 0 1  90 deg. 1 0 270 deg. 1 1180 deg. (Note: MSB, left most bit, is always “first in time”) CDMA RWCode 32 chip RW code (15 dB nominal processing gain) Walsh generator:This results in RW codes: RW 0: 00000000000000000000000000000000 RW 1:01010101010101010101010101010101 . . . RW 31:01101001100101101001011001101001 (Note: With the exception of Base toSubscriber Differential Phase/Antenna Reference, an RW code is used foran entire burst frame.) Pseudo-Noise 512 chip Gold code, equivalent to 1(PN) code acquisition symbol (27 dB nominal processing gain): Sum of 2R9 maximal length PN codes with appended DC balance bit 7 codes arerequired for system deployment (maximum 7 frequency reuse) Chosen bycomputer search for lowest cross correlation 5 code repetitions perframe. (Note: Ensures compliance to FCC/ETSI spreading requirements)Symbol code 16 symbol Rev. sequence at symbol/RW repetition rate Normaloperations: 0000000000000000 Acquisition: 0101010101010101 Symbol/CodeApplied to I and Q quadrature legs of the Modulation modulated symbol:Spread signal = (Modulated Symbol) ⊕ ((PN ⊕ RW ⊕ (Symbol Code)))Code/Symbol Basestation: locked to network time (With Time TX and RXaligned) Distribution Subscriber: Slaved to network time as recovered atRX; TX offset from RX set by radio overhead commands from Base toSubscriber. (Note: Phase Lock of subscriber reference to recovered baseis required.) Subscriber {fraction (1/32)} chip minimum (i.e.independent TX/RX RX/TX Fine fine clock adjustment) Code Phase OffsetData None, if block codes are used Scrambling Digital Base See RFSpecification above Band Filtering Multiple 2 independent 32 KBPS or 1concatenated 64 Channel MODEM KBPS channel minimum (see Frame Structurefunction below)

Forward Error Correction

As addressed above in the discussion on co-channel interference (CCI),Forward Error Correction (FEC) is needed in the present implementation.Application of FEC to FDD cellular, WLL, and satellite links hastraditionally used convolution encoders with soft decision Viterbidecoders. With communications links in both directions being continuousand having duration of operation which greatly exceeds the requiredtrace back memory (typically 7 to 9 times the constraint length), theramp up and synchronization of the convolution decoder is typically notan issue. Combined with a lack of frame synchronization requirements fordecoding and typically 5 dB of coding gain for rate ½ codes, convolutionencoders are a natural choice. For burst or framed channels, block codeshave been found appropriate in particular applications. CD players, diskdrives, pagers, LANs, and other burst or frame oriented applications alluse block codes.

The recovery of CDMA codes and correlation measurements provides anindependent method of establishing the start of frame for application ofblock codes. The use of block codes provides the ability to easily tradeoff correction capability for latency. This in turn allows for the useof burst/packet messaging for control of the present invention.

One skilled in the art can implement various methods of forward errorcorrection. By means of illustration, burst forward error correction isused in the present TDD implementation of the present invention. Oneoption is presented in the following table.

(24,12) Bit extension of octal 5343 Golay polynomial extended (tripleerror correction) w/1/2 frame symbol Golay code interleaving

FEC is applied to specific fields/bits in the burst frame. The framestructure is described more fully below, however, for the presentdiscussion, it is sufficient to understand that the fields are dividedinto three groups:

1. Block FEC protected bits: 72 bits which carry traffic (voice or data)and telecommunications control

2. Soft FEC protected bits: 4 bits of radio overhead protected byseparate software FEC

3. Unprotected bits: 4 bits for guard, phase reference, and antennadiversity select (Note: as guard symbols are increased to accommodatelarger service radii, the bits also increase accordingly.)

One skilled in the art understands that there exist various othermethods of using forward error correction in a burst frame structure.However, for illustration purposes the (24,12) Golay FEC is discussed inmore detail as applicable to the present implementation.

The block-protected bits are divided into two 36-bit fields. Thisresults in three FEC blocks and 72 bits. At the transmitter, the 72 bitfield is interleaved to spread single burst errors across all three FECblocks where the interleaved bits are DQPSK modulated. At the receiver,the bits are demodulated, de-interleaved and decoded. By dividing theBurst into 2 fields, there results a 50% reduction in the interleaveddelay.

FIG. 4 illustrates the delays associated with the FEC processing. FECBlock Encode 700 and Decode 708 delays result in a 0.333 ms delay each.Interleave 702 and De-Interleave 706 delays result in a 1 ms delay each.And, the Inter-Burst 708 delay results in a 0.5 ms delay. The aggregatedelay is thus 3.166 ms.

The 3.166 ms delay is a worst case implementation. If a systematicencoder (i.e. GF(2) algebraic encoding) is used, the delay can beshortened to several symbols as opposed to a complete block resulting ina possible savings of 0.333 ms and a revised one-way delay of 2.833 ms.A similar implementation could be made for the decoder side, The use oferasures (3 value soft decoding, +1, 0, −1) or soft decision decoding isalso contemplated.

FIG. 5 illustrates the interleaver structure. A (6,12) interleaver, with6 Rows 800 and 12 Columns 802, is applied to the 3 concatenated encodedblocks. This structure results in spreading a burst of 7 errors to, atmost, 3 errors in any one block. The block decoder then exceeds theburst error capability of a Viterbi R=½, K=7 coding system for bursterrors.

The Radio Overhead channel is protected by a separate “soft encoding”.These fields are naturally interleaved by the frame structure andoperate at a nominal rate of 2 KBPS or less. The content of these fieldsprovides fine adjustments in TX time offset and power out of thesubscriber from the basestation. Because TDD operations allow for “openloop” TX power control and because of the fixed access nature of WLLsystems, only a few timing adjustments after initial acquisition arenecessary. Fine control of these properties greatly decreases theself-noise typical of all CDMA systems.

As fields discussed here are critical to a present implementation,enhanced FEC can be applied without impacting the performance or delayin the traffic bearing fields.

Burst Frame Structure

FIG. 6 illustrates the top-level TDD burst frame structure used in thepresent implementation. The present invention is based on a 1 ms burst,2 ms burst period TDD structure. At each burst period 900 and 902, up to32 simultaneous time synchronous CDMA channels can be transmitted ineach direction. The two 1 ms bursts 900 and 902 result in the aggregate2 ms frame period 904.

FIG. 7 illustrates FDD operation with this interface. With continuouslyconcatenated frame transmission or by sending 2 separate TDD channels inthe FDD duplex channels, FDD structures 1000 and 1002 are achieved.

The burst frame structure provides a digital transport for:

Standard Traffic channels which provide basic POTS or ISDN viaconcatenation of CDMA channels,

Acquisition and Pilot channels which operate at {fraction (1/16)} symbolrate and provides an additional 12 dB of processing gain (high gainsubscriber RX synchronization, and asynchronous low interferencesubscriber TX synchronization with the basestation under radio overheadlink control).

WLL System Control or Embedded Data (generally protected by HDLC/LAPDpacket structure),

FIG. 8 provides a detailed diagram of 3 frame structure types. Any ofthe 32 available CDMA channel codes can be used with these frameformats. Subscriber to Basestation Traffic Frame 1100 and Basestation toSubscriber Traffic Frame 1102 operate as standard voice trafficchannels. Acquisition and Pilot Frame 1104 is used to achieve receiverand transmitter synchronization. Control Data Frame 1106 and EmbeddedData Frame 1108 provide basestation control and subscriber accessfunctions as well as data service. Note that the frame structures havevarious fields which include the Guard (G) 1110, Differential PhaseReference (DR) 1112, Traffic (T) 1114, ISDN D or control messaging (D)1116, Radio Overhead (RO) 1118, and Control (C) 1120.

TABLE 5 G 1110: This field is used as a TDD channel guard Guard periodfor TX power ramp-up and ramp-down. Extended guard bands are providedfor subscriber transmit and for acquisition. DR 1112: This field is usedfor phase reference. An Differential absolute Phase 0 degree referenceis sent at Phase the start of any burst to initialize the ReferenceDQPSK differential detector at the receiver. The basestation sends 3 DRsymbols to allow the subscriber to make measurements of a diversityantenna at each received packet. This burst is always sent on RW 0 withall other RW codes disabled. The measurement sequence is as follows: 1)Switch to alternate antenna during guard symbol, 2) Measure alternateantenna during DR1, 3) Switch to primary antenna during DR2, 4) Measureprimary antenna during DR3 and continue demodulation, 5) If thealternate antenna is significantly better, swap alternate and primeantennas at next RX, and 6) Perform open loop TX power adjustment basedon new measurement of RX burst. T 1114: This field carriesTraffic/Bearer data and Traffic may contain encoded voice, data, or anyother data stream. The baseline system supports at 32 KBPS in a singlechannel. As described previously, this field is FEC protected. D 1116:ISDN This field functions as either an ISDN D D channel or (Q.931control messages) channel or a Proprietary proprietary control interfacewhich is a Control superset of Q.931. The channel provides for Messagingcall control and other associated system messaging during operations ofa CDMA traffic channel. The data in this channel is protected byHDLA/LAPD transparent frame formatting. The baseline system supports 4KBPS throughput for a single channel. This field is FEC protected asdiscussed previously. RO 1118: This field supports low level physicallayer Radio control of subscriber TX power and TX timing Overhead offsetby the basestation. This field is only used with Traffic andAcquisition/Pilot CDMA channels. For these channels a one-to- one linkexists between the subscriber and the basestation. Either 2 KBPS or 1.5KBPS throughput are provided based on rate 1/2 coding. This field isprotected by “soft FEC” as discussed previously. C 1120: This field isused for in basestation system Control control, software download,subscriber line concentration access request, subscriber controlresponse and bi-directional embedded data service. Note that this fieldis a combination of the T and D fields of the Traffic frames 1100 and1102 and can provide data service at 36 kbps (i.e. 32 + 4 kbps). Allpacket traffic in these channels is intended to be transmitted usingHDLC packet framing. Two types of packets are: Standard LAPD forbasestation to subscriber incoming call initiation (Q.931), softwaredownload, OAM&P, system flow control messages, and all embedded datamessages. Note that it is necessary to fragment data to 128 byte orless. Burst control packets for single burst frame messages which aremodified HDLC packets transmitted in a single frame and consist of 7Eflag, 4 byte message, 2 CRC 16 bytes, 7E flag, and trailing 1's. Thesemessages are for embedded packet ACK, NACK, RTS, and CTS, subscriber tobase access messages, subscriber to base control responses, andbasestation to subscriber start of access frame messages.

As shown in FIG. 8, the subscriber-to-basestation packet implements 3guard, G, symbols and the basestation-to-subscriber packet implements 1guard, G, symbol. In the 36 kilobit per second system presently beingdescribed, such an implementation allows for servicing a service radiusof approximately 5.5 kilometers. Because of the nature of ruralapplications of WLL systems, it is necessary to provide service tolarger areas. As such, the present invention allows for the extension ofthe guard symbols by 2 (+2), 4 (+4) and 8 (+8) symbols as necessary.Thus the present 80 symbol field would be extended to 82, 84, and 88symbols, respectively. To implement such changes, the clock frequency isincreased appropriately (ie, 2.5%, 5%, and 10% respectively. Slightlywider bandwidth is necessary for increasing the clock speed, but thebenefits, where necessary, are appropriate. Such is the application ofthe present embodiment, however, one skilled in the art can apply theseconcepts so as to provide service to any of a large number of radii inan area of service.

TCP/IP Fragmentation

As discussed above, the packet structure of a WLL system is notoptimized for the length of TCP/IP data. Where TCP/IP typically uses 512bytes of data plus packet header information, the message may be toolarge for digital wireless implementations. Furthermore, long packetscause delay and have higher fail probability that would requireretransmission. To resolve this problem, fragmentation is implementedwhere the original packet is split into multiple fragments with aminimum of 1 byte and a maximum of 64, 128,and 256 bytes based on abaseline 32 kilobit per second WLL system. The size is capable of beingdynamically changed to improve efficiency. It should be noted thatfragmentation complicates the design by requiring, among other things,more memory and CPU cycles for the packet assembly and disassembly (PAD)functions.

FIG. 18 illustrates how the typically long TCP/IP message is fragmentedinto pieces of appropriate length for transmission in the WLL system ofthe present invention. The TCP/IP message is divided up into severalfragments of maximum size that can be handled by the WLL system. Thelast fragment is not necessarily of maximum length depending on thelength of the message. The fragments are then encapsulated with certaininformation including: an address byte; a fragment sequence number andcontrol; fragment length; a packet fragment; and, 16 or 32 bit CRC. Theaddress byte, ADDR, is effectively the logical connection to thereceiver unit and the customer premise interface. Where the IP addresspacket fragment controls distribution of information to one or more IPnetwork users connected to the customer premise interface on the WLL.The fragment sequence number and control byte, SEQ/C, providesinformation on the position of the fragment sequence in relation to thewhole packet. Where fragment lengths may differ, the fragment length,LEN, provides the length of the fragment in decoded bytes. The fragmentof the packet data then follows where the various fragments can beconcatenated to reproduce the entire data packet. Finally, CRCinformation is sent.

Protocols Channel Description

A single WLL TDD frequency/sector provides a pool of 32 independent CDMAchannels. This pool of channels is divided into smaller pools of CDMAchannels providing specific service between the subscriber terminal andthe basestation. Based on system traffic demands (call activity), usertraffic channel requirements (36 kbps embedded data, 32 kbps voice, 64kbps voice, etc.) and RF interference levels, the number of CDMAchannels assigned to any pool can be varied to meet demands. Thiscapability is termed “Dynamic Pool Sizing”, and represents a fundamentaladvantage of the present invention. FIG. 9 illustrates an example ofchannel pool allocation for a single sector/frequency implementation.With Dynamic Pool Sizing, the number of channels assigned to aparticular function at any given time may be different than in FIG. 9.

Table 6 provides a description of the channel function and content. Inmany cases, functions are logically paired between the subscriber andthe basestation, but as described previously, asymmetrical channelallocation may be utilized in providing data service.

TABLE 6 Base Station This channel is assigned to CDMA channel 0 Pilot1200 typically operates continuously. The TX: channel is used by allsubscribers to Basestation to achieve full receiver synchronizationprior Subscriber to switching over to the Basestation Control channel towait for a specific acquisition grant command. The radio overheadcarried by the this channel can be used to ensure valid synchronizationby any subscriber. This channel is paired with Subscriber Acquisition onthe same CDMA channel. In case of complete system failure or power down,Dynamic Pool Sizing may allocate additional Pilot/Acquisition CDMAchannels for rapid service recovery of the system. Subscriber Thischannel is paired with Basestation Acquisition Pilot. A subscriber caninitiate 1202 transmitter synchronization with the base TX: station onthis channel after receiving an Subscriber to acquisition grant commandfrom the Basestation Basestation Control channel. The subscriberacquires Radio Overhead synchronization of the paired Basestation Pilotand performs transmitter power and time offsets based on commands fromthe basestation. Once acquisition is complete, the subscriber returns toBasestation Control channel for Authentication and normal operations.When synchronization is achieved and the duplex link is established, thetransmitter power, transmitter power relative to receiver power andtransmitter time offset relative to receiver time can be retained as“warm acquisition parameters”. This channel can also be used to“refresh” synchronization of any active subscriber in the system. Incases of complete system failure or power down, Dynamic Pool Sizing mayallocate additional Pilot/Acquisition CDMA channels for rapid servicerecovery of the system. Basestation This channel is assigned to CDMAchannel 1 Control 1204 typically operates continuously. This TX: channelprovides the following functions: Basestation to Establishes Start ofAccess Frame using a Subscriber single Burst Control packet (Once every128, or 256 TDD time slots = Access frame length [0.25 to 0.5 seconds])Authenticates subscriber using LAPD Sets up incoming calls (base tosubscriber) using LAPD Sets up outgoing calls based on subscriberrequest in Access Frame Slot using LAPD Provisions using LAPD ProvidesOAM&P functions using LAPD Downloads software using LAPD Providesembedded packet service using LAPD This channel is paired withSubscriber Access. Subscriber This channel is assigned to CDMA channel 1Access 1206 typically operates continuously. This TX: Subscribe channelis used for outgoing call set-up to Basestation and to respond to LAPDcommands sent on the Basestation Control channel. Only burst controlpackets are sent by subscribers. The Access frame is either 128 or 256slots long based on the level of concentration in the deployed cell. Twotypes of slots are provided: Fixed assigned poll slots for outgoing callestablishment, emergency calls, and response to specific commands. Fastresponse slots (every 16th slot, 0, 16, 32, 48, . . . ) for immediateresponse to incoming call message by the called subscriber. A subscriberis assigned a specific slot in the Access frame during the Acquisitionprocedure. This channel is paired with Basestation Control on the sameCDMA channel. Traffic 1208 CDMA traffic channels are a pooled resourceBi-directional and are dynamically allocated under link, Basestationcontrol. These channels are Subscriber to assigned as a single CDMAchannel pair for Basestation a complete traffic and control link betweenand the subscriber and the basestation. Once Basestation to handed overto a traffic channel, all call Subscriber control and call tear down isestablished via the D channels embedded with this link. As theprovisioning of a subscriber to 1 or more user interface lines is knownby the basestation, the D channel can be used for call establishment ofone or more secondary lines while a line is in use. Dynamic switching ofrates for 32 K to 64 K can also be supported. Micro-ChannelMicro-channel bank requires 1 CDMA channel Bank 1210 for bi-directionalconcentration control Bi-directional (superset of V5.2) and 1 to N MCBtraffic link, channels. Using Dynamic Pool Sizing, the Subscriber tonumber of MCB channels can be changed based Basestation on demand. TheEnhanced Radio Unit (ERU) and acquisition procedures use the Pilot andBasestation to Control channels as previously described. Subscriber Oncesynchronization is established, the ERU is assigned to the MCBbi-directional concentration channel (a single CDMA channel) and behaveslike a point to point microwave link. Embedded Embedded packet servicefor up to 8 users Packet 1212 is provided on a single CDMA channel.B-directional Dynamic Pool Sizing may be used to allocate link,additional channels as more subscribers Subscriber to request dataservice. The characteristics Basestation of this channels are verysimilar to that and of the Traffic channel described above Basestationto except that it is not necessary to assign Subscriber these channelsas pairs -- the present invention provides for asymmetrical dataservice. A data access protocol is provided for: Service access requestand authentication Assignment by the basestation to a specific CDMAchannel or aggregate channel (i.e. using multiple CDMA channels)Assignment of a virtual wireless access identifier Mapping of thevirtual wireless access identifier to a physical address (typicallyTCP/IP or novel IPX) Packet Assembly and Disassembly (PAD) functions atboth basestation and subscriber including fragmentation buffers andprocedures for transport over the WLL Modified token ring or Request-To-Send/Clear-To-Send (RTS/CTS) protocol is used The basestation performsprotocol conversion to a standard network protocol and provides adigital interface (typically fraction E1/T1 via frame relay) to a routerat the central office for transport on the network. The subscriberstation has a modified customer premise interface (CPI) specifically fordata access. Specialized software is also provided to the subscriber forproper data transfers.

TDD CDMA Acquisition Protocol

The following describes the TDD CDMA acquisition scheme of the presentinvention. The frame structure is depicted in FIG. 15 where the waveformis split equally between a 1 msec basestation-to-RU burst and a 1 msecRU-to-basestation burst. When the guard band is taken into account, eachburst duration is 800 μsec long leaving 200 μsec of guard.

There are three unknown parameters to TDD CDMA receiver synchronization:(1) carrier frequency, (2) PN phase, and (3) frame phase. The first stepis to conduct an iterative procedure with both carrier frequency and PNphase to achieve local PN sequence synchronization. Once the local PNsequence is synchronized to the transmitted PN sequence, it is stillnecessary to align the TDD frame.

PN sequence synchronization is an iterative process spanning allpossible frequency offsets and phase shifts. FIG. 16 describes theprocess in a flowchart. The first step is to determine the frequencyoffset range for the receive carrier. For example, given 2 ppm, 2.4 GHzcrystals on both the transmitter and receiver, the maximum carrierfrequency error is 9600 Hz. Moreover, the QPSK tracking discriminatorcan only operate under a maximum frequency offset of {fraction (1/8 )}thof a constellation spin, or 5 kHz/8=625 Hz. Thus, when transitioningfrom acquisition to code tracking, the RF carrier frequency must not befarther than 625 Hz off. Stepping in 1 kHz steps from f_(nominal)−10 kHzto f_(nominal)+10 kHz satisfies the above constraint.

This is an example where a typical system may have ±2 ppm at thebasestation and ±8 ppm at the subscriber station which can result in ±24kHz. Aging can add ±0.5 ppm to this budget per year.

FIG. 17 shows the CDMA acquisition hardware where, initially, the DSPsets the frequency, f, of the down converter to equal f_(nominal−)10kHz. Then, it enables the 4 correlators to accumulate over a full TDDframe. The correlators encounter a receive signal for 800 μs somewherein that 2 ms TDD frame. If the Rx PN phase equals the local PN phase inone of the 4½ chip paths, the DSP reads a high correlation from one ofthe 4 correlators (early, punctual, late, or extra late). Otherwise, theDSP reads very low correlations. After each TDD frame, the DSP advancesthe phase of the PN generator by 4½ chips (or 2 chips) and correlatesagain. It repeats this process until it has tried all possible local PNphases:

Chip iterations per carrier frequency

=512 chips (or 256 TDD frames)+clock drift factor

=512 chips+maximum drift in 256 TDD frames measured in chips 512chips+maximum clock drift 0.512 s

=512 chips+(100 ppm*2.56 Mchips/s)*0.512 s

=512+131

=643 chips

=322 correlations

An enhancement to this architecture provides for more correlators andresults in improvement by covering decreased chips per TDD frame. Forexample, increasing the correlators to 6 results in a 1.5 timesimprovement by covering 3 chips per TDD frame such that the iterationscalculated above result in 215 correlations—a significant reduction.

The DSP keeps a record of the maximum correlation and its location foreach of the 21 frequencies between f_(nominal)−10 kHz to f_(nominal)+10kHz. When this process is complete, the DSP chooses the frequency thatresults in the maximum correlation.

Once the frequency has been chosen, the DSP can concentrate on PN phasealignment. First, it searches the entire 643 chip window as describedabove. Once it finds the maximum correlation, it adjusts the PN phase tothe center of a smaller window, say ±30 chips. It then correlates fromPN phase_(nominal)−30 to PN phase_(nominal)+30 in single 2-chip steps,noting the maximum correlation and its index.

Note that the location of the maximum correlation in this second searchresults in an estimate of PN frequency offset. If the maximumcorrelation occurs in the middle of the second window, there is verylittle difference between the receive PN frequency and the local PNfrequency. If the maximum correlation is late, it indicates that thelocal PN frequency is lower than the received PN frequency. The oppositeis true if the correlation is early. This information can be used toadjust the frequency of the local PN clock.

The maximum correlation of the second search window is used to determinea threshold for the third and final PN search. Once again, the DSPadjusts the PN to the center of a very small window, say ±3 chips. Itthen correlates from PN phase_(nominal)−3 to PN phase_(nominal)+3 insingle 2-chip steps until it encounters a correlation greater than thethreshold. At this point, the PN codes are synchronized to within ½ chipso the DSP allows the local PN generator to free-run.

PN synchronization does not imply frame alignment since the PN sequenceis repeated 10 times over a TDD frame. To determine the correct framephase, the DSP determines if there is an appreciable receive signalduring each symbol by comparing the symbol correlations to a threshold.If the correlation is above the threshold, the frame is currently inreceive mode. Otherwise, it is in transmit mode. Quickly thereafter, thereceiver sees a pattern of 4 high correlations in a row (correspondingto the receive burst) followed by 6 low correlations in a row(corresponding to the transmit burst). Once the DSP has seen a patternof 6 low correlations, 4 high correlations, and 6 low correlations itknows to immediately set the frame phase to start at the beginning ofthe receive frame.

At this point the CDMA modem has acquired the receive burst. To remainsynchronized, the modem transits to tracking mode where the DSP usesearly/late to advance/retard code timing.

Acquisition and Call Processing

The following provides descriptions for subscriber acquisition,commissioning, and call processing. Before any subscriber can becommissioned for service, provisioning information for the subscriberRadio Unit must be entered into the basestation (unique ID, subscriberinterface(s) supported, etc.). Without this information, the subscribercan achieve initial synchronization but fails authentication and is,thus, denied call/service access to the system.

Assuming a subscriber has been properly installed, the subscriberinitiates a cold start acquisition process by successfully completingSubscriber Receiver Synchronization, Subscriber Transmittersynchronization, and Authentication. The following describes theprocedures involved in setting up voice service, however, it should beunderstood that the same procedures can be used to set up data service.The only differences occur when the user goes “off-hook” or “on-hook” onthe provided data interface.

FIG. 10 provides a flowchart of the Subscriber Receiver Synchronizationprocedure. At Step 1300, the subscribers tunes to a specified RFchannel. This step can be repeated to test all possible RF channels. Thesubscriber CDMA channel is then switched to Basestation Pilot (Step1302) and long PN timing is recovered (Step 1304). The RF frequencyerror is adjusted to zero (Step 1306) and both initial NCO and VCOsettings are saved for “warm start” (Step 1308). A Burst Frame alignmentis then performed (Step 1310). Synchronization is confirmed by decodingof and alignment to the Radio Overhead frame (Step 1312). All data inthe Radio Overhead frame is ignored until transmitter synchronization isachieved. The subscriber switches CDMA channels to Basestation Control(Step 1314) and confirms frame alignment (Step 1316). The subscriberthen waits for a transmitter synchronization message (Step 1318) whereprovisioned serial number is used to direct the subscriber to initiate.

FIG. 11 provides a flowchart of the Subscriber TransmitterSynchronization procedure. Upon receipt of a valid transmittersynchronization message (Step 1400), the subscriber switches to theBasestation Pilot channel (Step 1402). The subscriber aligns timing tothe Radio Overhead frame (Step 1404) and sets the transmit delay (Step1406) to the median time offset RX frame alignment. Transmitter power isthen ramped up (Step 1408) to −15 dB of nominal power (full rate channelor −27 dB of low rate power). The open loop power control is used toadjust the power level based on every received frame. At the BasestationRX correlators are offset (Step 1410) from the transmitter frame by themedian time delay. The Basestation then transmits coarse offset (Step1412) on the Radio Overhead channel and returns receiver correlators(Step 1414) to the system TX/RX alignment position. Offset istransmitted until full link is established or time out occurs. When thesubscriber receives the coarse offset message (Step 1416), thesubscriber sets transmitter to coarse time delay (Step 1418). When theBasestation receives the subscriber Radio Overhead message (1420), theBasestation signals that the link is established with differential powerand fine time adjustments set to zero (Step 1422). Through a handshakeprocedure, the subscriber confirms the link (Step 1424). The Basestationand subscriber then initiate differential phase and power adjustmentsuntil a complete alignment is achieved (Step 1426). These values aresaved for “warm start”. At this point, either a Time-out (Step 1428)occurs or the subscriber is returned to the Basestation Control channel(Step 1430) for Authentication.

FIG. 12 provides a flowchart of the Authentication procedure. Uponsuccessful completion of Subscriber Transmitter and ReceiverSynchronization, the Control channel publishes a temporary slotassignment (Step 1500) to the newly synchronized subscriber until thesubscriber responds (Step 1502) or a time-out occurs (Step 1504). If thesubscriber responds, the subscriber switches to the Basestation Controlchannel (Step 1506) and listens for the slot assignment (Step 1508).Upon receipt, the subscriber sends an acknowledgment (Step 1510) duringthe assigned time slot. At this point, bi-directional authenticationmessages are transferred (Step 1512) and, if successful, the subscribernow begins normal operations and the assigned slot is made permanent fornormal operations (Step 1514). If this procedure is unsuccessful, theuser is locked out of the system (Step 1516).

Normal operations consists of incoming and outgoing call establishment,software download, and OAM&P functions. A subscriber may exist in threestates: STANDBY state, OPERATION IN PROGRESS state or ACTIVE (Traffic)state. If a subscriber provides more than one line of service, status iskept on the individual lines. During either an incoming or outgoingcall, the Radio Overhead channel is used to provide fine adjustment oftransmitter power and timing and to provide the values needed for “warmstart”.

FIG. 13 provides a flowchart for the procedure to establish incomingcalls over the Basestation Control channel. If the subscriber status isACTIVE (Step 1600) or all channels are in use (Step 1602), the call isrejected. Otherwise, a CDMA channel is removed from the pool of idlechannels (Step 1604) and an incoming call message is sent by theBasestation (Step 1606). At this point the subscriber status isOPERATION IN PROGRESS. Upon receipt of the incoming message (Step 1608),the subscriber posts a confirmation on the earliest available FASTresponse slot (Step 1610), and posts the message a second time onfollowing slot (Step 1612). The subscriber then switches to the postedchannel (Step 1614) and synchronizes to the radio overhead channel (Step1616). Upon posting of the incoming call message, the Basestationinitiates D and Radio Overhead messages on the Traffic channel (Step1618). Bi-directional D and RO communications are established (Step1620) and final call set up is completed (Step 1622). At this point, thesubscriber status is ACTIVE. If this procedure fails or a time outoccurs, the network is sent a busy signal (Step 1624), otherwise, anormal call is completed (Step 1626). When an on-hook situation isdetected (Step 1628) at either end, call tear down procedures areinitiated (Step 1630) and the subscriber returns to the BasestationControl channel with STANDBY status.

The procedure for-outgoing calls is quite similar to incoming calls,however , the tight time constraints imposed by the network interface isnot required (rapid dial tone in approximately 1 second is a reasonableoperations goal). FIG. 14 provides a flowchart for the procedure toestablish outgoing calls. Upon detection of the off hook condition andsubscriber status is STANDBY (Step 1700), the subscriber posts anoutgoing call message (Step 1702) at the next assigned time slot (Notethat FAST slots are not used for outgoing calls). Upon receipt of theoutgoing call message (Step 1704), the Basestation checks to see if allthe traffic channels are being used (Step 1706). If all channels are inuse, the basestation posts a busy message and the subscriber appliesbusy tone (Step 1708). If a channel is available, the base posts achannel available message twice (Step 1710). The subscriber status isthen OPERATION IN PROGRESS. The subscriber switches to the postedchannel (Step 1712) and synchronizes to the Radio Overhead channel (Step1714). Upon the posting of the incoming call message, the Basestationinitiates D and Radio Overhead messages on the Traffic channel (Step1716). Bi-directional D and RO communications are established (Step1718) and final call set up is completed. At this point, the subscriberstatus is ACTIVE. If this procedure fails or a time out occurs, thenetwork is sent a busy signal (Step 1720), otherwise, a normal call iscompleted (Step 1722). When an on-hook situation is detected at eitherend, call tear down procedures are initiated (Step 1724) and thesubscriber returns to the Basestation Control channel with STANDBYstatus.

While in the STANDBY state, any number of overhead functions areperformed. However, the following priority must be observed:

1. Broadcast Control messages to one or more subscribers to ceasetransmission, to stop and resynchronize, and to set up power and timing(if subscriber transmission power deviates by over +/−¼ chip or +/−1 dBin open loop operations calibration messages are sent).

2. Subscriber to Basestation emergency call override. Digit captureallows automatic call drop of as many traffic channels as are requiredfor emergency service requests

3. Incoming calls from the network. In the case where the subscribergoes of hook in the middle of incoming, call establishment (i.e., glarecondition) is pushed through to the subscriber without ring generation.

4. Subscriber to base standard calls.

5. All other operations.

Software download is performed over the basestation control channel bydividing the firmware image into small packets and using positiveacknowledgment (ACK) by the subscribers and retransmission of imagepackets until complete images are available at all subscribers. Eachpacket and the entire image should be protected by software checksums aswell as HDLC formatting.

Virtual LAN Protocol

As has been described above, the virtual LAN of the present inventionrequires certain provisioning. The customer premise interface must beequipped with a dedicated data port; the basestation must be capable ofprocessing and routing data through a telecommunications network; theuser must have an internet service provider that assigns the user withan IP address which the present invention associates with a virtual IPaddress. With these provisions met, the virtual LAN implements uniqueprotocols to established LAN service. As shown below, the LAN protocolof the present invention is similar to the voice protocols of thepresent invention.

A service request is first initiated by the subscriber. Note that if acustomer is using a business server at the customer premise interface,interface will be active at all times. Once the service request isinitiated, the control channel is used for access request as in thevoice service. The basestation then provides an access grant where alocal logical number is provided for MAC protocol and a CDMA code isalso provided. The subscriber then acknowledges the basestation's accessgrant. Upon a failure the sequence is repeated until successfulcompletion or timeout.

In the LAN CDMA channels, service association and authenticationprotocols are implemented as follows. The basestation requests anassociation packet. The subscriber station replies with a logical numberand IP and subscriber station number. This step is repeated untilsuccessful or a timeout is reached. The basestation then authenticatesthe IP or subscriber station number against a provision table previouslyestablished. Upon successful authentication, the basestation grantsaccess. Alternatively, if the user is not provisioned properly, thebasestation denies access.

Under normal operations the basestation transmits outbound packets andcontrol information and the subscriber station replies in a token ringmanner. The subscriber station transmits fragmented information asdetailed previously in this specification. A positive ACK/NACK protocolis applied to all fragments unless the message is a broadcast message.Retransmission of TCP/IP data is as required in the TCP/IP protocol.

In order to improve efficient use of resources it may be necessary toimplement timeout and disconnect procedures where the user isdisconnected after no data is transmitted for a specified amount oftime. Upon such an occurrence a disaccociate message is sent so as toreset the stations. Upon further need for data access, the user'sservice re-established using the protocol just described.

The present invention is designed to meet the timing, electrical, andassociated protocols required to support the standardized interfaces ofthe customer premise equipment as well as the telecommunicationsnetworks. Furthermore, the RF spectrum that the present invention usesis a highly regulated, scarce and valuable resource. For the most part,operators have to either purchase the spectrum outright or operate in ashared band. In either case, efficient modulation techniques, digitalpulse shaping, and proper cell/frequency planning are required tomaximize spectral utilization. Concentration is a fundamentalrequirement of any commercially viable WLL and played a critical role inthe design of the present invention. Future network interfaces (V5.2 andGR-303) provide naturally concentrated interfaces and are within theambit of the present invention.

It should be appreciated by those skilled in the art that the specificembodiments disclosed above may be readily utilized as a basis formodifying or designing other WLL systems for carrying out the samepurposes of the present invention. For example, the coding andmodulation scheme may be changed as hardware requirements necessitate.Similarly frame structures may be changed to meet certain specializedneeds. It should also be appreciated by those skilled in the art thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention as set forth in the appended claims.

What is claimed is:
 1. A wireless telecommunication system to allowindividual subscribers in an area of telecommunications service accessto a telecommunications network comprising: at least one subscriberinterface, the at least one subscriber interface connected to one ormore items of customer premise equipment, the customer premise equipmentcapable of transmitting and/or receiving voice and/or data signals; theat least one subscriber interface having a modulator for modulatingvoice and/or data signals from the customer premise equipment into aform suitable for transmission over a wireless communication channel;the at least one subscriber interface having a demodulator fordemodulating a signal received over a wireless communication channelinto a voice or data signal; a base station interface, the base stationinterface connecting the wireless telecommunication system to thetelecommunication network; the base station interface having a modulatorfor modulating voice and/or data information from the telecommunicationnetwork into a form suitable for transmission over a wirelesscommunication channel; the base station interface having a demodulatorfor demodulating a signal received over a wireless communication channelinto a form suitable for transmission over the telecommunicationnetwork; a plurality of wireless communication channels, a firstsub-pool of the wireless communication channels being used forcommunication between the base station interface and the plurality ofsubscriber interfaces, a second sub-pool of wireless communicationchannels being used for communication between the base station interfaceand at least one enhanced subscriber interface; and at least oneenhanced subscriber interface including an enhanced radio unit; theenhanced subscriber interface being capable of handling the secondsub-pool of communication channels; the enhanced subscriber interfacefurther being capable of handling a plurality of active customer premiseequipment.
 2. The system of claim 1, wherein the enhanced suscriberinterface handles voice service.
 3. The system of claim 1, wherein theenhanced suscriber interface handles data service.
 4. The system ofclaim 1, wherein the enhanced suscriber interface handles multimediaservice.
 5. The system of claim 1, wherein the enhanced suscriberinterface handles video service.
 6. The system of claim 1, wherein theenhanced suscriber interface handles concatenation of a number ofchannels to form a high rate hyperchannel.
 7. The system of claim 1,wherein the enhanced suscriber interface handles voice, data, multimediaor video service simultaneously.
 8. The system of claim 1, wherein theenhanced suscriber interface increases or decreases the number channelsin the second sub-pool without interruption of service.
 9. The system ofclaim 1, wherein the number of channels in the second sub-pool is chosenso as to provide a specified quality of service as measured by a ratioof a number of blocked subscriber communications versus a number ofsubscriber communications attempted and wherein the enhanced subscriberinterface handles which attempted subscriber communication is to beblocked.
 10. The system of claim 1, wherein the number of channels inthe second sub-pool can be changed dynamically depending upon thechannel usage and/or environmental conditions and wherein the enhancedsubscriber interface determines when the number of channels in thesecond sub-pool should be changed.
 11. The system of claim 1, whereinthe enhanced suscriber interface services a high occupancy residentialor business unit.